A GRAY EVOLUTIONARY LENS
Old age ain't no place for sissies.
— Bette Davis
I vaguely remember my father having black hair. Being the youngest of four and born to older parents, I recall my most vivid memories to be of him having silver hair and mustache. He was sort of a mix between Clark Gable and Cesar Romero. Lucky Mom. However, as he got older, it wasn't difficult to see changes in the way he looked, spoke, moved, and acted. Except for mild diabetes and minor back issues resulting from a tumble off a ladder, he sported relatively good health for most of his life. By the time I started attending UCLA as an undergraduate, I noticed that some of his tastes and habits had begun to change. Instead of having a beer or two with my uncles, he opted for coffee. He passed on the late-night movie, went to bed a bit earlier, and napped more often. Although he was a modest smoker in his younger years, I don't remember him picking up a cigarette after the age of forty or so. In his later years, he spent much of his time working with my older brother in their workshop. As he occupied himself with one craft project or another, I saw that he was starting to hunch slightly while he worked, as if he was in a slow but constant struggle against gravity. In his sixties, he was much thinner compared to his earlier cinematic appearances in family home movies. I suspect much of his weight control was the result of my mother's close attention to his diet because of his diabetes. However, I am certain he was simply declining as a result of aging.
Charles Darwin and my father both lived to the age of seventy-three. Both married, fathered children, had their share of health issues, and were outlived by their wives. While my father did not write any books, venture to the Galápagos, or have the fame of Darwin, both ultimately succumbed to the effects of aging and died of heart failure. Though my father's passing was sudden, his death was not shocking. He was a great husband, father, and grandfather. As he aged, his life changed and he adjusted with dignity and a wry sense of humor that was often capped by a rolling of the eyes and a smile. Though he was not a biologist and not very familiar with physiology, hormones, or the biological bits and bobs of aging, I am certain that during his later years he understood that he was not the man he had been when he was twenty. Seventy-three trips around the sun is an accomplishment for most men around the world. As with Darwin, Pop lived a long, rich life and was loved by many. By any measure, evolutionary or otherwise, my father was a success.
Thousands of miles away in South America, other men in the forests of eastern Paraguay were living parallel lives. Cuategi is a bit younger than my father but not by much. As a man from the Ache people, who until the 1960s and 1970s were full-time nomadic foragers with very limited contact with the outside developed world, he spent most of his time searching for food, keeping his family safe, and coping with the daily microdramas that are commonplace in all small communities. He made and stoked fires from damp wood, drank wild yerba mate from the Ilex paraguariensis bush (now widely available in the organic food section of your local supermarket), fashioned archery bows from palm wood using a modified land snail shell as a hand planer, and devoted many days to the pursuit of capuchin monkeys (Cebus capucinus), white-lipped peccary (Tayassu pecari), and paca (Cuniculus paca), to name just a few of the items on the Ache menu.
Cuategi fathered several children, became a grandfather, and experienced significant life changes, not the least of which was making first peaceful contact with the outside world when he was well into adulthood. Up until his twenties, he and his band lived solely within the confines of the Paraguayan forest, away from modern settlements, actively avoiding loggers, farmers, and poachers who sometimes ventured into the jungle — although from time to time he and his band were not above the occasional incursion into a farmer's manioc field when hunger made it a necessity. As he got older, his beard turned gray, he contracted and survived leishmaniasis resulting in the destruction of his upper palate, and lost more than a few teeth. Eventually he and other members of his small community decided to leave the forest to make first peaceful contact with a family of Norwegian missionaries, eventually settling into semipermanent housing on their land near the Ñacunday River in eastern Paraguay close to the Brazilian border. Today their life is taken up by the daily chores of farming, some modest foraging, and spending time with family and friends. In his seventh decade of life, Cuategi and his band now cope with the daily challenges of adjusting to a world full of cell phones, the Internet, bills, and diabetes. The rapidity and intensity of their transition from forest-dwelling, full-time foragers to blue-jeans-wearing surfers of the Web is dizzying and unprecedented in human evolution. Most are now on Facebook.
On the other side of the world in eastern Africa, a male chimpanzee makes his way through the Ugandan forest. He is large, robust, and emboldened by the life experience that comes from surviving four decades in the wild, avoiding poachers' snares and other potential threats. Although in relatively good health for his age, he is clearly more feeble compared to other males in their teens and twenties. The fur on his chin is white. He knows the importance of alliances and staying clear of neighboring chimpanzee groups that would readily beat him to death if he were foolish enough to be caught alone. During his twenties, he managed to hold the alpha position in his group and fathered several offspring but never devoted any time to caring for them. His life was preoccupied with staying out of the crosshairs of rival males and nurturing coalitions with other males who allowed him to outlive his rivals. As he becomes old and weak, he will disappear into the forest, never to be seen again. A primatologist may find his bones.
The lives of my father, Cuategi, and the chimpanzee could not be more different. Yet beyond their particular life conditions and environmental circumstances, the biological and social forces that shaped their journey of aging are similar. Three important factors unite them and how they aged. First, they are males. Belonging to sexually reproducing species, their lives were significantly influenced since conception by the union of their parents' X and Y chromosomes as well as the subsequent cascade of hormonal and other developmental changes that come with being a male. This is not to say that their genes determined their destinies or daily life decisions, but their sex chromosomes and male phenotype certainly had significant roles in their lifetime development. Second, the biology of their aging was shaped by evolution by natural selection. As a product of evolution, their aging processes share important similarities as a result of their common ancestry. Yet humans and chimpanzees are different because of the environmental and social challenges that face each species. As a species, human males also face common and distinct environmental and social challenges that shape their behavioral and reproductive strategies as they age. Finally, male aging is unique compared to that of women because of the different constraints that emerge from our reproductive and metabolic biology.
In this book, based on those three premises, I will argue that an evolutionary lens is vital for understanding the biology of male aging. Moreover, I will contend that evolution has shaped male health, influenced human evolution as a whole, and will guide where we are heading as a species. In essence, Darwinian fingerprints are on every aspect of male aging. But why should one care? There are numerous books on health and well-being as well as evolutionary biology. But understanding the evolution of male aging goes beyond health and well-being. There are other important reasons to understand male aging from a Darwinian perspective.
Besides putting some modest polish on our scientific literacy, there are other ways in which understanding male aging can be informative and more than a bit interesting. If you bought this book, it is probably because you have some interest in the topic. You're an older man, the partner of an older man, or someone who has a general interest in the evolution of the human condition. Perhaps as an aging man, you are looking for some insights into why and how your body is changing. That's a perfectly reasonable motivation. If your partner or other loved one is an aging man, you may be wondering why he is spending more time in his favorite chair, snoozing, or otherwise changing from when he was younger. An entire chapter is devoted to changes in muscle mass, the dreaded love handles, and the hormones that are responsible. You may also be interested in more serious aspects of health like prostate disease, erectile dysfunction, or male pattern baldness. Is testosterone supplementation safe? What does it mean to have low testosterone levels? What are "normal" testosterone levels for older men? These are all rational incentives to read this book.
But to gain a deeper understanding of health and illness, one needs evolutionary theory. The reason is that natural selection does not create perfect organisms, and imperfect organisms tend to have a nasty habit of accumulating defects, aging, and eventually dying. Men and women are also subject to different selection pressures that contribute to sex differences in aging and life span. That is, during our evolutionary past and arguably up to the present, men and women have faced challenges that are unique to their sex. Drawing on examples from reproduction, for women, these include childbirth and lactation. For men, it has been competition with other males and evolving ways to be attractive mates. Evolving optimal traits that can cope with the effects of aging is in itself a major challenge.
Virtually every physical trait is a compromise in response to the development and needs of other traits. Sometimes traits complement each other and actually promote the effectiveness of the function of other traits. Often the investment or expression of one trait will compromise the function of another. These compromises or "trade-offs" lead to imperfections that result in physical degradation, illness, and eventually death. Trade-offs are a primary driver of aging. Men and women contend with different trade-offs and therefore exhibit different patterns of aging and death. A male body needs to make crucial decisions about how to allocate calories and other resources to promote reproductive success. In Darwinian evolutionary theory, surviving is not enough. Survivorship is only time in service of trying to produce offspring and push one's genes through to the next generation. As we will see, men pay a significant tax in the form of shortened life spans in order to include their genes in subsequent generations. What is interesting about men, however, is that they may have developed unique solutions to maintain the ability to father offspring at older ages and address the challenge of somatic degradation and aging. More on that later.
Besides questions of health, well-being, and how evolutionary theory can shed light on these important issues, I would offer that there are other deeper and compelling reasons for taking an interest in aging males. If you are reading this, it is safe to assume that, like the author, you are human. Therefore, how evolution shaped our ancestors into the beings that they were and how that resulted in you reading these words is, in my humble opinion, bloody interesting. How did we emerge as the dominant species on the planet? Yes, there are far more beetles on the earth than people, but one cannot ignore how we have diverged from our other ape cousins and evolved traits that are unexpected for a large-bodied great ape. Simply by sheer numbers and our ability to shape our environment, for better or worse, we are pretty successful as a species. I will argue that to get to this point in our evolutionary history, traits associated with male aging may have been leveraged to facilitate the evolution of human-specific traits in all individuals, both men and women. These traits were vital to our success as a species.
Fast-forward to the present, and we can readily agree that the world is clearly run and controlled by men. I am certainly not condoning this reality; I am simply making a statement based on fact. Most of those men are also older, say, over the age of fifty. With very few exceptions, virtually all heads of state, chief executive officers, and individuals who wield socioeconomic and political power are older men. Clearly men have leveraged economic, social, and political power in their favor. How did this come to pass, what makes them tick, and how did they evolve? The acquisition of this power and influence is through competition with other males and active and passive subjugation of women's political and socioeconomic power. For anyone who is interested in gender equity or motivated to pursue it, I would suggest that understanding the evolution of older men and how they arrived at this point in history would be at best strategic and at least somewhat useful. But before we delve into these complex and nuanced questions, we will have to define what we are assessing in men.
WHAT IS AGING?
Understanding the specifics of aging in men requires that we get a handle on what we are putting under the evolutionary microscope. Aging is more than simply the passage of time or the number of candles on a birthday cake. Aging is a physical process that affects individual men and is guided by a number of factors including physics, genes, disease, and other environmental challenges. From a genetic perspective, the process of aging shares similarities with the biology of height. Both have a high degree of heritability, which means that the genetic complement of your parents has a significant predictive effect on your own height, or in this case how you age. The association is certainly not perfect, but the relationships are pretty strong with genetic variation accounting for 20–25 percent of the chance one will live past the age of eighty. However, despite this high degree of heritability, no single gene or suite of genes accounts for this relationship, at least none of which we are aware. Genes are an important aspect of aging, but their expression often depends on environmental cues and the action of other genes. In addition, genes are carried around within individuals, populations, and species that interact with each other in crucial ways. We need a more holistic approach to understand the whole evolutionary picture.
Zooming out from the individual, we can also observe aging from a higher perspective, one that examines male life span and mortality both within and between populations and species. Men have longer life spans compared to male chimpanzees, for example; the probability of dying at various ages is remarkably similar. Comparative analysis of the demography between us and our closest primate relative reveals that there are deep evolutionary roots that guide male mortality, aging, and life span. In addition to our similarities to other primates and mammals, humans are also unique in ways that are clearly evident, such as how we walk, our lack of body hair compared to other primates and mammals, our large brains, and language, just to name a few spiffy characteristics. While these are all qualities that would make any self- respecting primate proud, there are other traits that allow scientists to assess human uniqueness on a more fundamental level. These characteristics are called "life history traits," which emerge from a branch of evolutionary theory called, not surprisingly, life history theory. In essence, this theory is an extension of evolutionary thought that provides scientists with a way of studying the evolution of different species by comparing basic traits that all organisms have in common. Of particular interest for the purposes of this book is the process of aging. All organisms deteriorate to some degree with time and are faced with the constraints created by this degeneration. While the entire body ages at once, different parts can age at different paces and in different ways. With life history theory we can ask: Are certain characteristics of aging in men unique to humans or are they common to other organisms? How has aging affected other life history traits in humans such as reproductive effort in both males and females? Addressing these questions also allows researchers to determine whether a trait is the result of some biological constraint in males or if it recently emerged in humans, perhaps as a result of changes in environment. These are deep, juicy questions.